Experiments are described to determine the cardiovascular control mechanisms of the marmot (Marmota flaviventris). Acute experiments are performed to determine the effectiveness of reflex responses to a pressor agent (phenylephine) and a depressor agent (nitroglycerine) when the baroreceptors and cardiopulmonary receptors are eliminated sequentially. Chronic experiments are performed with isolated carotid sinus preparations seasonally and during hibernation. The studies should indicate the seasonal alteration of blood pressure control and indicate the contribution of carotid sinus mechanisms to the control of blood pressure by the hibernating animal.